Semiconductor device including built-in crack-arresting film structure

ABSTRACT

A wafer-to-wafer semiconductor device includes a first wafer substrate having a first bonding layer formed on a first bulk substrate layer. A second wafer substrate includes a second bonding layer formed on a second bulk substrate layer. The second bonding layer is bonded to the first bonding layer to define a bonding interface. At least one of the first wafer substrate and the second wafer substrate includes a crack-arresting film layer configured to increase a bonding energy of the bonding interface.

DOMESTIC PRIORITY

This application is a Continuation of U.S. patent application Ser. No.15/209,269; published as US 2016-0322324 on Nov. 3, 2016; which is aDivisional of U.S. patent application Ser. No. 14/543,986, filed Nov.18, 2014 which issued as U.S. Pat. No. 9,536,853; Issue Date: Jan. 3,2017, the disclosure of which is incorporated by reference herein in itsentirety.

BACKGROUND

The present invention relates generally to semiconductor devicefabrication, and more specifically, to semiconductor devices formedusing wafer-to-wafer bonding techniques.

Wafer-to-wafer bonding is a three-dimensional integration and/orpackaging process that is typically used to improve packaging size andprotect sensitive internal structures of the semiconductor device fromenvironmental influences such as, for example, temperature, moisture,high pressure and oxidizing species. Referring to FIG. 1, asemiconductor device 100 formed according to a conventionalwafer-to-wafer bonding processes typically includes a first wafer 102 abonded to a second wafer 102 b. The first wafer 102 a and the secondwafer 102 b define an oxide-oxide bonding interface 104 formedtherebetween.

Conventional semiconductor devices 100 formed according to conventionalwafer-to-wafer bonding processes are susceptible to the formation ofuniform cracks 108 in one or more oxide layers 106 a/106 b defining theoxide-oxide bonding interface 104 (see FIG. 2). In the case of FIG. 2,the crack has been initiated in the process of measuring bond energy byusing the well-known Maszara method. The crack length extending alongthe X-axis from edge towards center can be determined and the bondenergy can in turn be determined by inserting a thin blade to initiate acrack form the edge of the bonded wafer pair. The Maszara methoddescribes the relationship of the crack length and bonding energy as:

$\begin{matrix}{{\gamma = \frac{3\mspace{14mu}{Et}^{3}h^{2}}{32\mspace{14mu} L^{4}}},} & {{Equation}\mspace{14mu}(1)}\end{matrix}$where, t is the wafer thickness, h is the thickness of the blade, and Lthe length of the induced crack.

Longer bond cracks suggest a weaker bonding process, which isundesirable. The uniform cracks 108 extend deep into the oxide layer ata distance (d1) and indicate a pulling/peeling separation phenomenonbetween the opposing oxide layers 106 a/106 b bonded at the oxide-oxidebonding interface 104. The pulling/peeling separation is typically suchthat little force is required to separate the two opposing conventionalsemiconductor wafers 102 a/102 b at the oxide-oxide bonding interface104. This can result in delamination and process yield losses duringdownstream processing with respect to wafer-scale bonding andmultistacking.

Conventional methods for improving wafer-to-wafer bonding processes aredirected to enhancing the cohesive and adhesive bonding energy of thespecific oxide layers 106 a/106 b that define the oxide-oxide bondinginterface 104. For example, various materials having increased toughnesshave been selected to form the individual oxide layers 106 a/106 b in anattempt to prevent the formation of uniform cracks. According to otherconventional methods, various surface chemistries have been applied tothe individual oxide layers 106 a/106 b in an attempt to strength theoxide material and achieve increase the bonding energy at theoxide-oxide bonding interface 104.

SUMMARY

According to at least one embodiment of the present invention, awafer-to-wafer semiconductor device includes a first wafer substratehaving a first bonding layer formed on a first bulk substrate layer. Asecond wafer substrate includes a second bonding layer formed on asecond bulk substrate layer. The second bonding layer is bonded to thefirst bonding layer to define a bonding interface. At least one of thefirst wafer substrate and the second wafer substrate includes acrack-arresting film layer configured to increase a bonding energy ofthe bonding interface.

According to another embodiment, a semiconductor wafer comprises anoxide layer formed on an upper surface of a substrate layer. Thesubstrate layer and oxide layer each extend along a first axis to definea length and a second axis opposite the first axis to define athickness. A crack-arresting layer is formed on an upper surface of theoxide layer. A bonding layer is formed on an upper surface of thecrack-arresting layer. The crack-arresting layer is configured toinhibit formation of at least one uniform crack in the bonding layer.

According to yet another embodiment, a method of fabricating asemiconductor device comprises forming a first semiconductor waferincluding a first bonding layer on a first crack-arresting film layer.The method further includes forming a second semiconductor waferincluding a second bonding layer. The method further includes bondingthe first bonding layer to the second bonding layer such that a strongerbond is induced at a bonding interface defined by the first and secondbonding layers.

Additional features are realized through the techniques of the presentinvention. Other embodiments are described in detail herein and areconsidered a part of the claimed invention. For a better understandingof the invention with the features, refer to the description and to thedrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter which is regarded as the invention is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The forgoing features are apparent from the followingdetailed description taken in conjunction with the accompanying drawingsin which:

FIG. 1 is a cross-sectional view of a conventional semiconductor deviceformed according to a conventional wafer-to-wafer bonding process;

FIG. 2 illustrates a uniform crack formed in an oxide layer of asemiconductor wafer forming a conventional wafer-to-wafer semiconductordevice;

FIGS. 3-5 are a series of views illustrating a process flow of forming asemiconductor wafer according to a non-limiting embodiment of theinvention, in which:

FIG. 3 is a cross-sectional view of a semiconductor wafer including abulk substrate layer having an oxide layer formed on an upper surfacethereof;

FIG. 4 illustrates the semiconductor wafer of FIG. 3 having acrack-arresting film layer formed on an upper surface of the oxidelayer; and

FIG. 5 illustrates the semiconductor wafer of FIG. 4 having a bondinglayer formed on an upper surface of the crack-arresting film layer.

FIG. 6 illustrates a branched crack formed in a bonding layer of awafer-to-wafer bonded semiconductor device formed according to anon-limiting embodiment of the invention;

FIG. 7 illustrates first and second semiconductor wafers formedaccording to a wafer-to-wafer bonding process of the invention andarranged prior to being bonded to one another; and

FIG. 8 illustrates the first semiconductor wafer bonded to the secondsemiconductor wafer following to a wafer-to-wafer bonding process thatforms a semiconductor device having increased bonding energy at anoxide-oxide interface according to a non-limiting embodiment of theinvention.

DETAILED DESCRIPTION

With reference now to FIG. 3, a first semiconductor wafer 200 forforming a wafer-to-wafer semiconductor device is illustrated accordingto a non-limiting embodiment. The first semiconductor wafer 200 includesa bulk substrate layer 202 having an oxide layer 204 formed on an uppersurface thereof. The bulk substrate layer 202 extends along a first axis(X-axis) to define a length and a second axis (Z-axis) perpendicular tothe first axis to define a height (i.e., thickness). According to anon-limiting embodiment, the bulk substrate layer 202 is formed from,for example, silicon (Si).

The oxide layer 204 is deposited on the bulk substrate layer 202 using achemical vapor deposition (CVD) or low pressure chemical vapordeposition (LPCVD) process, for example, and is typically formed fromvarious materials including, but not limited to, tetraethylorthosilicate (Si(OC₂H₅)₄) to form silicon dioxide (SiO₂) layer. Thethickness of the oxide layer initially deposited on the bulk substratelayer 202 can range from 300 nanometers (nm) to 10 microns (μm), forexample.

The oxide layer 204 can further be planarized using achemical-mechanical planarization (CMP) process as understood by one ofordinary skill in the art. The surface resulting from the CMP processprovides a smooth and flat topography that enhances formation of abonding layer thereon, which is discussed in greater detail below. Thethickness of the oxide layer 204 following the planarization process canrange from approximately 100 nm to approximately 5000 nm, for example.

The bulk substrate layer 202 and/or the oxide layer 204 can includevarious front end of line (FEOL) components and/or back end of the line(BEOL) components (not specifically shown in FIG. 3). The FEOLcomponents may include, but are not limited to, transistors, capacitors,resistors. The BEOL components may include, but are not limited to,electrically conductive contacts, insulating/dielectric layers, metallevels, conductive vias/wirings, and bonding sites.

Referring to FIG. 4, the semiconductor wafer 200 of FIG. 3 isillustrated having a crack-arresting film layer 206 formed on an uppersurface of the oxide layer 204. The crack-arresting film layer 206 maybe formed from one or more various low-dielectric (i.e., low-k)materials including, but not limited to, octamethylcyclotetrasiloxane(OMCT), and can be deposited using, for example, a CVD or LPCVD processas understood by one of ordinary skill in the art. The crack-arrestingfilm layer 206 has a thickness ranging from approximately 10 nm toapproximately 200 nm.

Referring now to FIG. 5, a bonding layer 208 is formed on an uppersurface of the crack-arresting film layer. The bonding layer 208 isformed from, for example, a low temperature oxide (LTO) layer 208. Inthis manner, on the top surface of the semiconductor wafer is formed amulti-layer bonding stack that has a thickness extending along theZ-axis, which includes a crack-arresting film layer 206 configured toinhibit cracking and thus increase the bonding energy between a pair ofbonded semiconductor wafers as discussed in greater detail below. TheLTO layer 208 is deposited on the crack-arresting film layer 206 using aCVD or LPCVD process, for example, and is formed from various lowtemperature oxide materials including, but not limited use of silane(SiH4) and other silicon precursors of the silanes family to form thedesired low-temperature oxide by CVD or LPCVD. The LTO layer 208 has athickness ranging from approximately 30 nm to approximately 500 nm, forexample.

It is appreciated that the LTO layer 208 can be activated prior toperforming a wafer-to-wafer bonding process using, for example, a wetactivation process or a plasma activation process. The wet activationprocess includes application of a hydrogen fluoride (HF) solution,hydrogen chloride (HCl) solution, or ammonia (NH₃) solution on to theLTO layer 208. Alternatively, the plasma activation process injectsnitrogen, oxygen, and/or carbon ions into the LTO layer 208. It isappreciated that a de-ionization (DI) rinse process may be performedfollowing the plasma activation process. The DI rinse process caninclude a solution doped with carbon dioxide (CO₂), for example, toremove the electrostatic charge from the surface of the LTO layer 208.

According to a non-limiting embodiment, the thickness of the LTO layer208 is equal to, or substantially equal to, the thickness of thecrack-arresting film layer 206. In this manner, unexpected results arerealized in that crack-arresting film layer 206 and the LTO layer 208are prevented from overwhelming or acting against one another in termsof relative stress/strain. Accordingly, crack inhibition in the LTOlayer 208 is enhanced, thereby enhancing the bonding energy at theoxide-oxide bonding interface of a wafer-to-wafer bonded semiconductordevice by significantly reducing the probability and the extent ofcrack-driven failure and delamination.

Conventional semiconductor devices obtained through conventional oxidewafer bonding exclude a crack-arresting film layer in the bonding stack.Consequently, these conventional semiconductor devices have weakerbonding energy at the bonding interface as evidenced by large, uniformcracks 108, especially at the bonded wafer pair edge (see FIG. 2). Theselarge uniform cracks 108 are indicative of lower bonding energy betweenopposing bonding layers, thereby pointing to easier separation ofconventional semiconductor wafers 102 a/102 b at the bonding layerinterface 104 (see FIG. 1), which is undesirable.

At least one non-limiting embodiment of the invention, however, includesan LTO layer 208 (i.e., bonding layer 208) formed on an upper surface ofa crack-arresting film layer 206. The crack-arresting film layer 206inhibits cracking in the LTO layer 208 of the semiconductor wafer 200.In this manner, cracks are inhibited from propagating deep in to the LTOlayer 208 once initiated. When measured by the Maszara method, theinhibition of cracks from progressing into the LTO layer 208 causes anycracking that may occur to be confined within a narrower edge area wherethe crack was initiated. This signifies that a stronger force would berequired to separate a bonded pair of wafers from each other at thebonding interface. That is, the crack-arresting film layer preventscracks from propagating further toward the center of the bonded waferstructure in contrast to cracks 108 that extend along a single axis(i.e., the X-axis) such as shown in FIG. 2. The cracks induced whenvarious embodiments of the disclosure are implemented are thereforeshorter than the longer uniform cracks found in bonding layers ofconventional wafer-to-wafer semiconductor devices. That is, the crackspropagate into the bonding layer, e.g., LTO layer 208, at a distance(d2) that is less than the distance (d1) of uniform cracks 108 formed inconventional semiconductor wafers. Accordingly, the semiconductor wafer200 according to at least one embodiment of the invention has anenhanced and more reliable bonding interface, which increases thebonding energy at the oxide-oxide interface of a wafer-to-wafer bondedsemiconductor device, as described in greater detail below. This reducesthe probability of delamination and thus minimizes process yield lossesform the bonding process.

As illustrated in FIG. 6, the inhibition of crack propagation in the LTOlayer 208 (i.e., bonding layer) is evidenced by the formation narrowercracks 210 confined more to the edge of the wafer, as opposed to thewider cracks 108 formed in the oxide layer 106 a/106 b of conventionalwafer-to-wafer semiconductor device 100 (see FIG. 2). That is, thecombination of the crack-arresting film layer 206 and the LTO layer 208according to at least one embodiment of the invention inhibits crackpropagation.

Turning to FIG. 7, a first semiconductor wafer 200 a and a secondsemiconductor wafer 200 b are arranged with respect to one another priorto performing a wafer-to-wafer bonding process according to anon-limiting embodiment of the invention. The first semiconductor wafer200 a and the second semiconductor wafer 200 b are each formed accordingto the process flow shown in FIGS. 3-5 described in detail above.Accordingly, the first wafer 200 a and the second wafer 200 b eachinclude a bulk substrate layer 202 a/202 b, an oxide layer 204 a/204 bformed on an upper surface of a respective bulk substrate layer 202a/202 b, a crack-arresting film layer 206 a/206 b formed on an uppersurface of a respective oxide layer 204 a/204 b, and a LTO layer 208a/208 b (i.e., bonding layer) formed on an upper surface of a respectivecrack-arresting film layer 206 a/206 b.

Turning now to FIG. 8, the LTO layer 208 a of the first semiconductorwafer 200 a is bonded to the LTO layer 208 b of the second semiconductorwafer 200 b according to a low-temperature wafer-to-wafer bondingprocess. In this manner, a wafer-to-wafer semiconductor device 212 isformed according to a non-limiting embodiment of the invention.According to a non-limiting embodiment, the low-temperaturewafer-to-wafer bonding process includes an initial bonding operationperformed at room temperature, followed by a permanent anneal operationperformed at temperatures of approximately 350 degrees Celsius (° C.) orless. These low temperatures achieve various performance enhancementsincluding high wafer alignment accuracy, high bonding energy, and highthroughput, all of which are not realized by high temperature bondingprocesses (i.e., at temperatures in excess of 350° C.).

Due to the crack-arresting film layer 206 a/206 b formed in each of thefirst and second semiconductor wafers 200 a/200 b, the wafer-to-wafersemiconductor device 212 according to at least one embodiment of theinvention has increased bonding energy at an oxide-oxide interface 214(i.e., bonding interface 214) defined by the opposing LTO layers 208a/208 b when compared to conventional wafer-to-wafer semiconductordevices 100 (see FIG. 1). According to an embodiment, the bonding energyat the oxide-oxide interface 214 ranges from approximately 15 J/m² toapproximately 90 J/m², as compared to up to about 2 J/m² withconventional oxide bonding layer stacks. It is appreciated that theincreased bonding energy realized by the wafer-to-wafer semiconductordevice 212 of the present invention can be measured and demonstratedaccording to the Maszara method as understood by one of ordinary skillin the art. As a result a greater amount of force is required to breakthe bonding energy that bonds together the opposing LTO layers 208 a/208b. In this manner, at least one embodiment of the invention reduces thesusceptibility of separation between the opposing LTO layers 208 a/208 bat the oxide-oxide bonding interface 214 thereby enhancing the overallreliability of the wafer-to-wafer semiconductor device 212.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of onemore other features, integers, steps, operations, element components,and/or groups thereof.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below are intended toinclude any structure, material, or act for performing the function incombination with other claimed elements as specifically claimed. Thedescription of the present invention has been presented for purposes ofillustration and description, but is not intended to be exhaustive orlimited to the invention in the form disclosed. Many modifications andvariations will be apparent to those of ordinary skill in the artwithout departing from the scope and spirit of the invention. Theembodiment was chosen and described in order to best explain theprinciples of the inventive teachings and the practical application, andto enable others of ordinary skill in the art to understand theinvention for various embodiments with various modifications as aresuited to the particular use contemplated.

The flow diagrams depicted herein are just one example. There may bemany variations to this diagram or the operations described thereinwithout departing from the spirit of the invention. For instance, theoperations may be performed in a differing order or operations may beadded, deleted or modified. All of these variations are considered apart of the claimed invention.

While various embodiments have been described, it will be understoodthat those skilled in the art, both now and in the future, may makevarious modifications which fall within the scope of the claims whichfollow. These claims should be construed to maintain the properprotection for the invention first described.

What is claimed is:
 1. A method of fabricating a semiconductor device,the method comprising: forming a first semiconductor wafer including afirst bonding layer on a first crack-arresting film layer, the firstbonding layer and the first crack-arresting film layer formed to ensurethat each comprises a same first thickness; forming a secondsemiconductor wafer including a second bonding layer; and bonding thefirst bonding layer to the second bonding layer such that a strongerbond is induced at a bonding interface defined by the first and secondbonding layers; and increasing the bonding energy at the bondinginterface in response to generating a stronger bond that inhibitsformation of long cracks in at least one of the first and second bondinglayers, wherein the forming a second semiconductor wafer includesforming the second bonding layer on a second crack-arresting film layer.2. The method of claim 1, further comprising interposing the firstcrack-arresting film layer between the first bonding layer and a firstbulk substrate layer of the first semiconductor substrate, andinterposing the second crack-arresting film layer between the secondbonding layer and a second bulk substrate layer bulk substrate layer ofthe second semiconductor substrate.
 3. The method of claim 2, furthercomprising forming the first and second crack-arresting layers from alow-dielectric material.
 4. The method of claim 3, wherein the low-kdielectric material is octamethylcyclotetrasiloxane (OMCTS).